The interaction of Type A behavior and social support in relation to the degree of coronary artery disease (CAD) severity was investigated. One hundred thirteen patients undergoing diagnostic coronary angiography received the Type A structured interview (SI) and completed a battery of psychometric tests, including the Perceived Social Support Scale (PSSS). Statistical analyses revealed a Type by social support interaction, such that the probability of significant CAD was inversely related to the level of social support for Type As but not Type Bs. Type As with low levels of social support had more severe CAD than Type As with high levels of social support. On the other hand, this relationship was not present for Type Bs. These results are consistent with the hypothesis that social support moderates the long-term health consequences of the Type A behavior pattern.